In electrophotography using an electronic copying machine or the like, a process has been well known and generally used widely wherein a developer is attached to an image carrier on which an electrostatic image has been formed, such as light-sensitive element, in the development step, transferred from the light-sensitive element to a copying paper in the transfer step, and then fixed on a copying paper in the fixing step. As developers for developing an electrostatic image formed on the latent image retaining surface, there have been known a two-component system developer consisting of a carrier and a toner and a one-component system developer (magnetic toner or nonmagnetic toner) requiring no carrier. The toner contained in these developers is normally made of finely divided colored grains mainly comprising a resin, a coloring material, etc. Toners are also divided into two groups, i.e., positively chargeable toner and negatively chargeable toner. As materials for providing the toners with positive or negative chargeability, there have heretofore been known general static electrification controlling agents, coating agents for providing the carriers with desired chargeability, etc.
As a process for the preparation of toner grains, there has been known a process which comprises blending various components such as binder resin and coloring material in proper amounts, kneading the mixture by a kneader or the like, cooling the material, grinding the material, and then sorting the material.
As a coloring material for black toner there is normally used powdered carbon black. However, the use of powdered carbon black is disadvantageous in that when the starting material of toner is handled in the process for the preparation of toner, much carbon black fly up, contaminating the body of the workers and polluting the circumstances of the workshop.
In order to eliminate these difficulties, the use of dry or wet process granular carbon black obtained by roll-granulation process has been proposed. For example, JP-A-2-291568 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a toner obtained by dispersing in a binder resin a granular carbon black having a grain size distribution of 140 .mu.m to 840 .mu.m and a bead hardness of 5 to 40 g. However, when kneaded by an ordinary method, such a granular carbon black cannot sufficiently get loose, causing maldispersion. Such a granular carbon black is also disadvantageous in that it doesn't have a proper stability in static electrification, causing image instability upon continuous copying or toner flying in the copying machine.
On the other hand, the use of carbon black masterbatched with a resin has been proposed. However, this approach leaves much to be desired due to the flying of carbon black upon masterbatching or complicated producing procedure (productivity drop).